Vertebral implants adapted for posterior insertion

ABSTRACT

Disclosed is an endoprosthetic implant for a human spinal disc. The structure of the implant allows it to be inserted posteriorly. This insertion is accomplished by performing a partial discectomy in the affected region. An intervertebral space is then created by removing the fibrocartilage between the facing surfaces of adjacent vertebrae. The implant is then inserted into the intervertebral space. The implant is thus adapted to replace damaged or worn intervertebral discs. Furthermore, the structure of the implant, and its posterior insertion, alleviate most spinal pathologies.

RELATED APPLICATION DATA

[0001] This application is a continuation-in-part of co-pendingapplication Ser. No. 10/449,733 entitled “Vertebral Implant withDampening Matrix Adapted for Posterior Insertion” filed on May 30, 2003,which is a continuation-in-part of application Ser. No. 10/021,319 filedDec. 7, 2001 and entitled “Vertebral Implant Adapted for PosteriorInsertion” (now U.S. Pat. No. 6,572,653). The contents of both priorapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to an endoprosthesis to replace anintervertebral disc. More particularly, the present invention relates toan endoprosthetic implant that is specifically designed to be insertedposteriorly.

[0004] 2. Description of the Background Art

[0005] The human spine is made up of twenty-four stacked segments calledvertebrae. Between adjacent vertebrae are small fibrocartilage cushionscalled intervertebral discs. These discs act as shock absorbers betweenadjacent vertebrae and permit the spinal column to bend. As bodilyforces are transmitted along spine, an individual disc can oftenencounter hundreds of pounds of force. Spinal forces are alsotransmitted by way of inferior and superior articular processes thatcontact each other at facet joints. Intervertebral discs and facetjoints are the two spinal mechanisms by which most spinal forces aretransmitted. Consequently, most spinal pathology occurs at theselocations.

[0006] For example, the fibrocartilage in the intervertebral discs oftenbecomes worn or damaged through wear, age and/or disease. This damagelimits spinal movements and can also result in pain as nerves becomepinched and swollen. Damaged fibrocartilage, in turn, increases thepressure that is otherwise encountered by the facet joint adjacent thedisc. This causes a premature wearing of the bone that makes up thejoint. Again, limited spinal movement and pain result.

[0007] One of the oldest methods of repairing damaged intervertebraldiscs involves fusing adjacent vertebrae by way of a bone graft. Suchmethods, however, have serious drawbacks in that the resulting fusedvertebrae limit the overall movement of the spine. Furthermore, once twovertebrae are fused, the pressures encountered by adjacent healthy discsis increased. This dramatically increases the likelihood that suchhealthy discs may become damaged and worn. Thus, the fusing of vertebraeoften propagates the malady it seeks to cure.

[0008] Prosthetics are also employed to alleviate damaged intervertebraldiscs. This involves the removal of damaged fibrocartilage. Thefibrocartilage is then replaced by an implant, typically formed from anelastomeric or an elastomeric composite. Prosthetic implants have thebenefit of providing a more full range of spinal movement over fusionprocesses. Nonetheless, the elastomerics typically wear out over thelife of the prosthetic. As a result additional medical procedures arerequired to replace the worn out prosthetic. Even prior to wearing out,elastomerics may simply wear unevenly, whereby the prosthetic providesan uneven resilient force between the vertebrae. This causes nerves tobecome pinched and swollen. Absent any type of wearing, elastomerics donot provide a cushioning effect that is equivalent to naturallyoccurring fibrocartilage. Forces not absorbed by the elastomeric arethen transferred to the adjacent facet joint. This results in prematurewearing of the joint.

[0009] An example of a synthetic intervertebral disc is disclosed byU.S. Pat. No. 5,458,642 to Beer, et al. Beer discloses the use of asynthetic intervertebral disc for implantation in the human body. Thesynthetic disc includes a polymeric core that is inserted between twoplates. Spring means are included in addition to the polymeric core.Each of the plates includes a tab that is secured to a vertebrae via ascrew.

[0010] Additionally, U.S. Pat. No. 6,231,609 to Mehdizadeh discloses adisc replacement prosthesis. The prosthesis includes screw threads whichengage the vertebrae. A vertical stiffness is obtained from a series ofcoil springs affixed between upper an lower rigid members. The coilsprings also provide assistance in resisting shear forces.

[0011] U.S. Pat. No. 5,556,431 to Büttner-Janz discloses anintervertebral disc endoprosthesis. The prosthesis includes two platesintermediate which a prosthesis core is included. The prosthesis core ismade from a polyethylene. Bone screws are utilized in securing the twoplates.

[0012] U.S. Pat. No. 5,824,093 to Ray discloses a prosthetic spinal discnucleus employing a hydrogel core surrounded by a constraining jacket.

[0013] Finally, U.S. Pat. No. 6,156,067 to Bryan, et al discloses aspinal disc endoprosthesis with concave surfaces. A resilient body isincluded intermediate the two surfaces.

[0014] Although each of the above-referenced inventions achieves itsindividual objective they all suffer from common problems. Namely, noneof the background art discloses an endoprosthesis which is specificallydesigned to be inserted posteriorly to thereby eliminate the most commonsource of spinal pathology.

SUMMARY OF THE INVENTION

[0015] It is therefore one of the objectives of this invention toprovide an intervertebral disc endoprosthesis which is specificallyadapted to be inserted posteriorly.

[0016] It is also an object of this invention to provide anintervertebral endoprosthesis which utilizes a mechanical spring toachieve a longer wear life and accommodate increased intervertebralforces.

[0017] Still another object of this invention is to provide anendoprosthesis which substantially eliminates most posterior spinalpathology.

[0018] Yet another object of this invention is to provide anendoprosthesis which eliminates the need for facet joints.

[0019] These and other objectives are accomplished by providing avertebral implant adapted for posterior insertion and designed toreplace the fibrocartilage between the facing surfaces of adjacentsuperior and inferior lumbar vertebrae. The implant includes two pairsof hydroxyapatite coated superior and inferior supports. Each supportincludes plate and lip portions. The lip portion is formed at a rightangle to the plate portion. In the case of the inferior support the lipportion is offset to one side. The plate portion of each support furtherincludes a plurality of teeth, a retainer, and a pair of tapering sideedges. Each plate portion is received within a channel formed within oneof the facing surfaces of the superior or inferior vertebrae such thatthe lip portions abut the posterior edge of the vertebrae. In the caseof the inferior support, the offset lip accommodates a vertebralpedical.

[0020] The implant additionally includes a pair of springs. Each springis formed from a plurality of oblong tapered coils. Each spring ispositioned between the side edges of opposing superior and inferiorsupports with the position of the spring being fixed by the opposingretainers. Each spring has an axial force under compression thatfunctions to drive the teeth of the opposing superior and inferiorsupports into the facing surfaces of the adjacent vertebrae.

[0021] The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription of the invention that follows may be better understood sothat the present contribution to the art can be more fully appreciated.Additional features of the invention will be described hereinafter whichform the subject of the claims of the invention. It should beappreciated by those skilled in the art that the conception and thespecific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] For a fuller understanding of the nature and objects of theinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawings in which:

[0023]FIG. 1 is a posterior view of the lumbar region of a human spine;

[0024]FIG. 2 is a detailed illustration taken from FIG. 1;

[0025]FIG. 3 is a side elevational view of the implant of the presentinvention fully inserted and is taken from line 3-3 of FIG. 2;

[0026]FIG. 4 is a cross-sectional view taken from line 4-4 of FIG. 2;

[0027]FIG. 5 is a top plan view of the superior support;

[0028]FIG. 6 is a side elevational view of one of the superior supports;

[0029]FIG. 7 is a bottom plan view of one of the superior supports;

[0030]FIG. 8 is an end view taken along line 8-8 of FIG. 6;

[0031]FIG. 9 is an end view of one of the inferior supports;

[0032]FIG. 10 is an end view of one of the inferior supports;

[0033]FIG. 11 is a side elevational view of one of the springs;

[0034]FIG. 12 is a plan view of one of the springs;

[0035]FIG. 13 is an exploded view of the implant system of the presentinvention;

[0036]FIG. 14 is an alternative embodiment of the implant of the presentinvention; and

[0037]FIG. 15 is a view taken from line 15-15 of FIG. 14.

[0038]FIG. 16 is a detailed view taken from FIG. 1 of an alternativeimplant system of the present invention.

[0039]FIG. 17 is a side elevational view of alternative embodimentdepicted in FIG. 16.

[0040]FIG. 18 is a top plan view taken along line 18-18 of FIG. 17.

[0041]FIG. 19 is a sectional view taken along line 19-19 of FIG. 18.

[0042]FIG. 20 is a sectional view of a lipless embodiment of the presentinvention.

[0043]FIG. 21 is a sectional view taken along line 21-21 of FIG. 20.

[0044]FIG. 22 is a posterior view of a screw shell embodiment of thepresent invention.

[0045]FIG. 23 is a sectional view taken along line 23-23 of FIG. 22.

[0046]FIG. 24 is a detailed view of one of the supports depicted in FIG.22.

[0047]FIG. 25 is a view taken along line 25-25 of FIG. 24.

[0048]FIG. 26 is a view taken along line 26-26 of FIG. 24.

[0049]FIG. 27 is a detailed view of the offset lip of one of theinferior supports.

[0050]FIG. 28 is an end view of one of the screws employed in the screwshell embodiment.

[0051]FIG. 29 is a side elevational view of the screw of FIG. 28.

[0052]FIG. 30 is a detailed view of the screw shell depicted in FIG. 23.

[0053]FIG. 31 is an end view of the screw shell taken along line 31-31of FIG. 30.

[0054]FIG. 32 is an exploded view illustrating the screw prior toinsertion into the screw shell.

[0055]FIG. 33 is a posterior view of yet another alternative screw shellembodiment.

[0056]FIG. 34 is a sectional view taken along line 34-34 of FIG. 33.

[0057]FIG. 35 is posterior view of a rocker embodiment of the presentinvention.

[0058]FIG. 36 is a sectional view taken along line 36-36 of FIG. 35.

[0059]FIG. 37 is a detailed view of one of the superior bearing surfacesof the embodiment depicted in FIG. 35.

[0060]FIG. 38 is a side elevational view taken along line 38-38 of FIG.37.

[0061]FIG. 39 is a detailed view of one of the inferior cups of therocker embodiment depicted in FIG. 35.

[0062]FIG. 40 is a side elevational view of the cup taken along line40-40 of FIG. 39.

[0063] Similar reference characters refer to similar parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0064] The present invention relates to an endoprosthetic implant for ahuman spinal disc. The structure of the implant allows it to be insertedposteriorly. This insertion is accomplished by performing a partialdiscectomy in the affected region. An intervertebral space is thencreated by removing the fibrocartilage between the facing surfaces ofadjacent vertebrae. The implant is then inserted into the intervertebralspace. The implant is thus adapted to replace damaged or wornintervertebral discs. Furthermore, the structure of the implant, and itsposterior insertion, alleviate most spinal pathologies. The implant ofthe present invention, and the manner in which it is employed, aredescribed in fuller detail hereinafter.

[0065] With reference now to FIG. 1, a posterior view of the lumbarregion of a human spine is depicted. The implant of the presentinvention 20 is specifically adapted for insertion between adjacentvertebrae in this lumbar region, specifically vertebrae L3 through S1.FIG. 1 illustrates some spinal anatomy including: the spinous process22; the superior and inferior articular process (24 and 26,respectively); the transverse process 28; pedicals 32 and facet joints34. FIG. 1 also illustrates a dissected area with the spinous process 22and superior and inferior articular processes (24 and 26) removed. Thisdiscectomy allows for the insertion of the implant 20 of the presentinvention in a manner more fully described hereinafter.

[0066]FIG. 2 illustrates the implant 20 positioned between facingsurfaces of adjacent superior and inferior lumbar vertebrae (36 and 38,respectively). The implant 20 includes: an upper, or superior, pair ofsupports 44; a lower, or inferior, pair of supports 46; and two springs48. As illustrated, each spring 48 is positioned between alignedopposing superior and inferior supports (44 and 46). Thus, an individualsupport column 50 is defined by a superior and inferior support (44 and46) interconnected by a spring 48. The preferred form of the implantincludes two support columns 50. However, the use of other numbers ofcolumns, such as one or three, is within the scope of the presentinvention.

[0067] Each superior support 44 is defined by: first and second ends (52and 54); a cantilevered plate portion 56; and a lip portion 58. Theplate portion 56 is cantilevered with the first end 52 being integralwith the lip portion 58 and the second end 54 being free. Thisarrangement allows the plate 56 to pivot with respect to the sides ofthe support. With reference now to FIG. 4, the relationship between thelip and plate portion (58 and 56) of a superior support 44 is depicted.Specifically, in the preferred embodiment, the lip portion 58 is formedat generally a right angle to the plate portion 56 at a first end 52 ofthe support 44. However, the exact angle between the lip portion 58 andthe plate portion 56 varies due to the cantilevered nature of the plate.With continuing reference to FIG. 4, the teeth 62 of the plate portion56 are depicted. These teeth 62 are formed by partially perforating theplate 56 to create protrusions which rise above the planer surface ofthe surrounding support 44. The teeth are preferably formed a 90 degreeangle with the plate portion 56. The teeth 62 enable support 44 toengage the vertebral body in a manner more fully described hereinafter.Thus, although the teeth 62 have been described as perforations, theycould be formed in a variety of different ways. For example, the teeth62 could take the form of sharpened protrubences that are fixed to anouter surface of the plate 56, such as by welding. Additionally, theteeth 62 can be arranged in a number of different positions, other thanthe aligned orientation depicted. In the unbiased state of plate 56, thebottom of teeth 62 are flush with the bottom edge of the support 44(note FIG. 6). The plate 56 further includes a retainer 64 formed in amanner similar to the teeth 62. Again, the retainer 64 is formed byperforating the plate portion 56 to create a raised protrusion. Theretainer 64 functions in constraining the spring 48 positioned betweenthe facing supports (44 and 46). Thus, the teeth 62 are raised in adirection opposite to the direction in which the retainer 64 is raised.That is, the teeth 62 are raised in the same direction of the lip 58,and the retainer 64 is raised in the opposite direction.

[0068]FIGS. 5 through 7 are more detailed showings of the superiorsupports 44. As can be appreciated from these figures, the superiorsupports 44 further include raised side edges 66 which taper along thelength of the support 44. That is, the side edges 66 are taller at thesecond end 54 of the support and taper toward the first end 52 of thesupport until the edges are planar with the plate portion 56. The raisedside edges 66, along with the retainer 64, function in locking thespring 48 into position between opposing supports (44 and 46).Furthermore, due to the cantilevered nature of the plate 56, the sideedges 66 are not connected with the edges of the plate 56.

[0069] With reference now to FIG. 4, the lower, or inferior supports 46,are described. In most respects, the inferior supports 46 are identicalto the superior supports 44. That is, the inferior supports 46 are eachdefined by a first and second end (68 and 72), a cantilevered plateportion 74, and a lip portion 76. Again, the lip portion 76 is generallyformed at a right angle to the plate portion 74 at the first end 68 ofthe support 46. Furthermore, the plate portion 74 includes a pluralityof teeth 78 and a retainer 82, both of which are formed in the mannerdescribed in association with the superior support 44. Each of theinferior supports 46 similarly include raised side edges 84 which taperfrom the second 72 to the first end 68 of the support 46.

[0070] With reference now to FIGS. 9 through 10, the primary differencebetween the superior and inferior supports (44 and 46) will bedescribed. That is, the lip 76 of the inferior support 46 is offset.More specifically, the lip portion 76 extends over only a portion of thewidth of the support 46. In the preferred embodiment depicted, the lip76 extends over approximately half of the width of the support 46. Assuch, the lip portion 76 is offset to one side. Furthermore, with thesupport 46 positioned on the vertebrae, the adjacent lips 76 arepreferably oriented toward the medial portion of the vertebrae. Thisoffset lip portion 76 is contrasted to the lips 58 of the superiorsupports 44 which extend across the entire width of the support 44 (noteFIG. 8). Thus, the lips 58 of the superior supports 44 are not offset.

[0071] The exact manner in which the supports (44 and 46) are positionedupon the facing surfaces of the opposing vertebrae is next described inconjunction with the exploded view of FIG. 13. As illustrated, the twosuperior supports 44 are secured to the surface 86 of the superiorvertebrae 36, and the inferior supports 46 are secured to the facingsurface 88 of the inferior vertebrae 38. More specifically, the twosuperior supports 44 are received within channels 92 that are formedwithin the inferior surface 86 of the superior vertebrae 36. Thesechannels 92 are preferably formed after the medical practitioner hasconducted the partial discectomy. The channels 92 are ideallydimensioned to specifically receive the width of the supports 44 and arerelatively shallow when compared to the overall height of the support44. The channels 92 aid in orienting the supports 44 and limiting theirmovement once positioned. After the channels 92 are formed the superiorsupports 44 are inserted over the surface 86 of the superior vertebrae36. This is done with the teeth 62 and lips 58 directed toward thevertebral body. However, at this stage the teeth 62 do not engage thevertebral body 36, insomuch as the plate 56 is unbiased and the teeth 62are flush with the lower surface of the support. As the supports 44 arepushed forward, the lip 58 of each support 44 will abut the posterioredge 94 of the vertebrae 36, which functions to properly orient thesupports 44 relative to the vertebral body 36. That is, each lip 58ensures that its corresponding support 44 does not extend too far ontothe vertebral body 36.

[0072] The above described insertion is repeated for the inferiorsupports 46. That is, the inferior supports 46 are inserted withinchannels 96 formed within the facing superior surface 88 of the inferiorvertebrae 38. Again, with the supports 46 inserted, the teeth 78 do notengage the vertebral body 38. After the discectomy, the inferiorvertebrae 38 will have remaining pedicles 32 preventing insertion of asupport with a full lip. Thus, the lower supports 46 include the offsetlip 76 that accommodates the vertebral pedicle 32. Nonetheless, eachoffset lip 76 still functions in limiting the insertion of itscorresponding support 46 into the corresponding channel 96.

[0073] The implant further includes springs 48 which are engaged betweenthe facing superior and inferior supports (44 and 46) as illustratedclearly in FIG. 13. Each support column 50 includes one spring 48, withtwo springs 48 being employed when two support columns 50 are used. Inpreferred embodiment, each of these springs 48 is a coil spring formedfrom a plurality of oblong coils. It has been found that the use of coilsprings increases the life of the implant over elastomeric springmembers. Preferably, each spring 48 is tapered from a second to a firstend. This spring geometry is illustrated in FIG. 11. Furthermore, FIG.12 is a plan view of the spring 48 showing its oblong or elongatedshape. The resulting free-standing orientation of the spring provides anarrower posterior profile 98 and a wider anterior profile 102. This, inturn, insures that the spring 48, when inserted, provides proper spinalcurvature.

[0074] With reference again to FIG. 13, the positioning of the springs48 between the supports (44 and 46) is described. Specifically, eachspring 48 is positioned such that the narrower end is adjacent theposterior edge of the spine and the wider end is adjacent the anterioredge of the spine. As indicated, this provides for proper spinalcurvature with the implant fully inserted. Each of the springs 48 isheld in place by opposing superior and inferior supports (44 and 46),and further by the upstanding side walls of such supports (66 and 84)and their retainer portions (64 and 82). More specifically, the sidewalls prevent the lateral movement of the spring 48 and the retainer (64or 82) precludes the spring from moving longitudinally. When properlypositioned, the springs 48 are under compression and generate an axialforce that serves to pivot the cantilevered plates 56 and 74 away fromtheir corresponding supports 44 and 46. As a consequence, the teeth 62and 78 are forced into the vertebral bodies (36 and 38). This preventsany lateral migration of the supports. When fully positioned the springsabsorb the forces between the superior and inferior vertebrae (36 and38) and take the place of the otherwise existing fibrocartilage.

Method of Insertion

[0075] The method by which the implant of the present invention isinserted is next described. In the first step a partial discectomy isperformed in order to gain posterior access to the damaged area. Thisdiscectomy involves removing the spinous process 22 and inferiorarticular process 26 from the superior vertebrae 36. The superiorarticular process 24 is also removed from the inferior vertebrae 38.This exposes the thecal sac, which is moved to gain access to thefibrocartilage. Next, the damaged fibrocartilage is removed to create anintervertebral space. This space provides access to the opposingvertebrae surfaces (86 and 88). Once the space is created the upper andlower channels (92 and 96) can be formed. Specifically, two oblongchannels 92 are formed within the surface 86 of the superior vertebrae36, and two oblong channels 96 are formed within the face 88 of theinferior vertebrae 38. These channels (92 and 96) are formed in facingrelation to one another. Thereafter, the two superior supports 44 areinserted into the channels 92 with the lips 58 functioning to limit theinsertion and otherwise properly orient the supports 44. The inferiorsupports 46 are then likewise positioned with the offset lips 76engaging the remaining pedicles 32 on the inferior vertebrae 38. Lastly,the two springs 48 are inserted. More specifically, the first spring 48is inserted intermediate the opposing superior and inferior supports (44and 46) and the second spring 48 is inserted between the remainingopposing superior and inferior supports (44 and 46). In each instance,insertion of the spring causes the teeth to engage the vertebral bodyvia action of the cantilevered plate.

[0076]FIGS. 14 and 15 illustrate yet another embodiment of the presentinvention. This embodiment is similar in most respects to the previouslydescribed embodiment. However, the two inferior supports 46 are eachprovided with a channel 104 formed along an interior edge. Thesechannels 104 are adapted to receive the sides of a spacer 106. That is,the opposing edges 108 of the spacer 106 are inserted within the facingchannels 104 of the inferior supports 46. This spacer 106 operates toabsorb any forces that would tend to operate individually on thesupports 46. Consequently, the spacer 106 functions in tying the twosupports 46 together such that they operate as an integral unit. Thespacer 106 is preferably positioned intermediate the channels 104 priorto insertion over the vertebral body.

[0077] All of the components of the above-described invention, that isthe superior and inferior supports (44 and 46), and the springs 48 aswell as the spacer 106, are preferably formed from a titanium alloy or astainless steel. Furthermore, each of these components is preferablycoated with a hydroxyapatite to promote bone growth about the componentswhen in place.

Dampening Matrices (FIGS. 16-19)

[0078] An alternative embodiment of the present invention is depicted inFIGS. 16-19. This alternative embodiment employs many of the samecomponents discussed with reference to FIGS. 1 through 15, as suchsimilar reference numerals are used to note similar components. Howeverthis alternative embodiment further includes two dampening matrices 120.Each matrix 120 utilizes an identical construction and is positionedbetween the superior and inferior supports (44 and 46) of the implant.The dampening matrices each act as a cushion between the adjacentsuperior and inferior lumbar vertebrae (36 and 38, respectively.)Accordingly, when the opposing vertebrae are compressed the matricesslow the rate of compression and absorb the forces and loads encounteredby the spinal tract. As noted below, this is achieved by the hydrogelcore 122 contained within each matrix.

[0079] Once the load is removed, resilient columns (or springs) providea return energy to reposition the adjacent vertebrae. This repositioningis achieved in the absence of loads upon the vertebral tract. In thepreferred embodiment, each of the resilient columns is positioned overand surrounds an associated dampening matrix. This arrangement isdepicted in FIG. 17.

[0080] In the preferred embodiment the dampening matrix is constructedfrom a hydrogel core positioned within a constraining jacket. Thisconstruction is similar to the prosthetic spinal disc nucleus disclosedin U.S. Pat. No. 5,824,093 to Ray, the contents of which areincorporated herein by reference. As noted in Ray '093, the hydrogelcore is formed as a mixture of hydrogel polyacrylonitrile. Inparticular, acrylamide and acrylonitrile are used. Furthermore theconstraining jacket is preferably a closed sack of a tightly woven highmolecular weight high tenacity polymerac fabric. The jacket preferablycontains openings that are large enough to allow bodily fluids to reactwith the hydrogel core, but are small enough to prevent the hydrogelfrom escaping. Thus the hydrogel, which has an affinity for imbibingwater, will deform and reform as necessary in order to accommodate andalleviate stresses and loads placed on the spinal tract. FIG. 19 is across sectional view illustrating the hydrogel core of the presentinvention.

[0081] After any loads applied to the hydrogel core are removed theresilient columns then return the opposing vertebrae to their properorientation. In this regard, the preferred resilient column has beendisclosed as a spring 48. However any other resilient tensioning devicesknown in the art can be employed. For example, the column can be formedfrom a leaf spring, coil spring, resilient coiled polymer or acontinuous polymer sleeve.

Lipless Embodiment (FIGS. 20-21)

[0082] The embodiment depicted in FIGS. 20-21 is the same in mostrespects to the implant described in conjunction with FIGS. 2 through13. The notable difference, however, is that the superior and inferiorsupports (132 and 134) have no lip portions hanging over the posteriorend of the upper and lower vertebral bodies. Consequently, asillustrated in FIG. 21, the first ends 136 of the superior and inferiorsupports (132 and 134) terminate adjacent the respective vertebralbodies. This “lipless” embodiment is advantageous because when theimplants are fully inserted the supports are unexposed. This embodimentalso weighs less than the embodiment of FIGS. 2-13.

[0083] Nonetheless, in this lipless embodiment there are no portions ofthe supports that overhang to prevent the supports from extending toofar towards the anterior end of the vertebral bodies. That is, there areno lips to prevent the over insertion of the support. Rather, thecorrect orientation between an individual support and its correspondingvertebral surface is achieved via channels 138 formed within thevertebral surfaces and teeth 142 formed within each support. Thesefeatures ensure a positive fit between vertebrae and prevent overinsertion.

[0084] In all other respects, the lipless embodiment is the same as theembodiment depicted in FIGS. 2-13. That is, both the superior andinferior supports (132 and 134) include a cantilevered lower surface 144into which a retainer 146 and a series of teeth 142 are formed. Eachsupport further includes tapering side edges 148. Insertion is achievedby performing a discectomy to create an intervertebral space as noted inconjunction with the primary embodiment. Thereafter, upper and lowerchannels 138 are formed in the surfaces of the vertebral body, with thesupports being positioned within these channels. Thereafter, springs 152are inserted bilaterally between the pair of superior and inferiorsupports (132 and 134). Again, as noted in conjunction with the primaryembodiment, each retainer 146 functions in preventing the movement ofthe spring 152.

Screw Shell Embodiment (FIGS. 22-34)

[0085] The next embodiment is described in conjunction with FIGS. 22-34.As with the primary embodiment, this embodiment includes two superiorsupports and two inferior supports (154 and 156, respectively) that arepositioned bilaterally in an intervertebral space. In this embodiment,two rounded inserts are secured between the supports. These inserts areinterconnected by way of a screw. Thus, each pair of inserts takes on a“screw shell” configuration.

[0086] The intervertebral space is again created in the manner describedin conjunction with the primary embodiment. Namely, a discectomy isperformed and two superior channels and two inferior channels are formedin the opposing faces of the intervertebral space. After the space iscreated, the superior and inferior supports (154 and 156) are insertedinto these channels. As with the supports in the primary embodiment, thesupports in the screw shell embodiment preferably include lips to limittheir insertion into the intervertebral space. Specifically, thesuperior supports 154 include full-width lips 158 that are dimensionedto engage the entire corresponding edge of the superior vertebrae. Theinferior supports 156 likewise include offset lips 162 as depicted inFIG. 22. These lips 162 encompass only a portion of the support width.In the preferred embodiment, the lips 162 extend over approximatelyone-half of the width of the support and are oriented towards the medialportion of the vertebrae. With this configuration, the inferior lips 162accommodate the pedicles (which may be partially dissected) extendingfrom the posterior face of the vertebrae. Furthermore, as noted in FIG.23, both the superior and inferior supports (154 and 156) can furtherinclude interior lips located at the second ends of each support thatprevent over insertion of the screw shell.

[0087] The supports of this embodiment differ from the primaryembodiment in that they each include a trough 164 formed along theirlengths. This trough, which is illustrated in FIG. 24, takes the form ofan arcuate segment, which is removed from the body of the support.Additionally, unlike the primary embodiment, the supports of thescrew-shell embodiment have neither a cantilevered floor or teeth. Thesearcuate portions of the supports permit proper placement of the screwshell inserts. That is, with the supports properly positioned in facingrelation, adjacent upper and lower troughs 164 form opposing arcuatesurfaces that are dimensioned to accommodate the upper and lower inserts(166 and 168, respectively)(note FIG. 23). The arcuate upper and lowerinserts (166 and 168), in turn, form a single shell 172. Two such shells172 are bilaterally positioned within the intervertebral space (noteFIG. 22).

[0088] The upper and lower inserts (166 and 168) are preferablyinterconnected by way of a screw 174. The interconnection is achieved bythreading the internal surfaces of the inserts in a manner that permitsa screw to be threadably positioned between the upper and lower inserts.This configuration allows for the lateral movement of the screw 174between either end of the screw shell 172 upon screw rotation. To enablethe screw 174 to be threaded into and out of the screw shell 172, eachincludes a hexagonal opening 176 at its end to facilitate physicianrotation of the screw via a matching key.

[0089] With continuing reference to FIG. 23, the arcuate upper and lowerportions of the screw shell are depicted. This cross-sectional viewillustrates the threaded internal surfaces of the inserts (166 and 168)and how they cooperate with a screw 174. The cross-section furtherillustrates how the arcuate portions of the inserts conform to thetroughs 164 of the superior and inferior supports (154 and 156). In thepreferred embodiment, the inserts are not permanently affixed to thecorresponding support, but rather simply rest within the correspondingtrough.

[0090] With reference now to FIG. 30, it can be seen that the anteriorend 178 of each insert is enlarged with respect to the posterior end.Accordingly, when the inserts (166 and 168) are positioned between thesupports (154 and 156) prior to screw insertion, the enlarged anteriorportions promote a lordosis of the spine. This configuration alsoprovides for an enlarged posterior opening of the resulting screw shelland a narrowed anterior opening. This “steady state” configuration canbe subsequently overcome by inserting a screw into the threaded interiorof the screw shell. Specifically, by driving a screw 174 from theposterior to the anterior region of the screw shell 172 the narrowedanterior opening of the screw shell is widened to thereby correct thelordosis (note FIG. 23). Proper spinal curvature is promoted by fullinsertion of the screw shell. Full screw insertion represents the finalsurgical step.

[0091] In an alternative embodiment of the screw shell, the lips of thesuperior and inferior supports (154 and 156) are removed. In thisembodiment, depicted in FIGS. 33-34, when the supports are inserted inthe intervertebral space, their posterior edges are flush with theadjacent vertebral bodies. Yet in another alternative construction, thescrew positioned between adjacent inserts is replaced by a helicalspring 182. This is similar to the prior embodiment, however, the springhas the advantage of both interconnecting the facing inserts andproviding resistance. As with the prior embodiment, each support wouldhave an interior surface that accommodates the periphery of the spring182.

Rocker Embodiment (FIGS. 35-40)

[0092] The final embodiment is depicted in conjunction with FIGS. 35-40.This embodiment again includes superior and inferior supports 186, whichare positioned within the opposing surfaces in the intervertebral space.However, in this embodiment, the supports 186 are fitted into channels184 that are both deepened and made more narrow. These channels 184accommodate a rail 188 running along the lower surface of each support186. It has been found that this rail 188 promotes a stableinterconnection between the support and vertebral surface. Also, as isknown in the art, the supports may include a hydroxoyappetite coating tofacilitate bone growth.

[0093] Upon each of the superior supports, an arcuate bearing surface192 is secured. This interconnection can be achieved via a suitableadhesive or mechanical fastener. This bearing surface 192 is preferablyformed from a suitable metallic or polyethylene material. Concavereceptacles 194, which are also formed from a metallic or polyethylenematerial, are similarly secured to the inferior supports. Thereceptacles 194 are dimensioned to accommodate each of the superiorbearing surfaces 192. In this manner, once these supports are secured,the interaction between the bearing surfaces and the cups allows for alimited posterior and anterior range of motion, while at the same timelimiting lateral motion.

[0094] The present disclosure includes that contained in the appendedclaims, as well as that of the foregoing description. Although thisinvention has been described in its preferred form with a certain degreeof particularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

[0095] Now that the invention has been described,

What is claimed is
 1. A vertebral implant for insertion between adjacentvertebrae having anterior and posterior faces comprising: a superiorsupport positioned upon a vertebral surface, the superior support havinga posterior edge which is flush with a posterior vertebral face, thesuperior support having an arcuate trough formed therein; an inferiorsupport positioned upon a vertebral surface in facing relation to thesuperior support such that a posterior edge of the inferior support isflush with a posterior vertebral face, the interior support having anarcuate trough formed therein; a two part shell positioned intermediatethe superior and inferior supports, the two part shell having arcuateupper and lower surfaces that correspond to the arcuate troughs formedwithin the superior and inferior supports; a threaded screw positionedwithin the two part shell, rotation of the screw causing its lateralmovement to thereby adjust the spacing between the two parts of theshell.
 2. A vertebral implant for insertion into an intervertebral spacehaving anterior and posterior areas comprising: superior and inferiorsupports positioned upon a vertebral surface in facing relation to oneanother, both supports being positioned in the posterior area of theintervertabral space; an insert positioned intermediate the superior andinferior supports, the insert adapted to absorb forces generated in theintervertebral space.
 3. The implant as described in claim 2 wherein theinsert is formed from upper and lower portions.
 4. The implant asdescribed in claim 3 wherein the upper and lower portions areinterconnected via a threaded element, wherein movement of the threadedelement causes relative movement of the upper and lower portions.
 5. Theimplant as described in claim 2 wherein the superior and inferiorsupports each include lips that are adapted to hang over an edge of thevertebral body.
 6. A vertebral implant specifically adapted forposterior insertion comprising: a superior support positioned upon avertebral surface, the superior support having a posterior edge which isflush with a posterior vertebral face; an inferior support positionedupon a vertebral surface in facing relation to the superior support suchthat a posterior edge of the inferior support is flush with a posteriorvertebral face; a member positioned intermediate the superior andinferior supports.
 7. The vertebral implant as described in claim 6wherein the member is in the form of a shell with arcuate upper andlower portions.
 8. The vertebral implant as described in claim 6 whereinthe member is a dampening matrix.
 9. The vertebral implant as describedin claim 6 wherein the superior and inferior supports include anoverhanging lip portion.
 10. The vertebral implant as described in claim6 wherein a spring is positioned between the superior and inferiorsupports.